JPH01110527A - Polyester polyol - Google Patents

Abstract

PURPOSE:To obtain the above polyol having a viscosity suitable for handling in the production of a polyurethane, low water absorption and excellent electrical insulation and free from emission of ill odor in processing, by esterifying a dimer acid with a castor oil polyol, etc. CONSTITUTION:The objective polyol can be produced by reacting (A) 1mol. of a dimer acid with (B) 1-2mol. of a castor oil polyol having <=2.5 functional groups per one molecule and (C) 1-0mol. of a polyol other than the component B (e.g., ethylene glycol), e.g., at 160-250 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to polyester polyols useful for urethane polyols and other uses, particularly polyurethanes that have easy-to-handle viscosity, low water absorption, and excellent electrical insulation properties. The present invention relates to polyols that can be provided.

Conventional Technology Traditionally, epoxy resins and silicone resins have been used as electrically insulating sealants to protect electrical and electronic components from vibrations and shocks, as well as from atmospheres containing moisture and dust, and to allow these components to perform their functions to the fullest. It is used.

However, epoxy resin has poor flexibility and has large internal stress and thermal contraction during curing, so there is a risk of wire breakage and electrolytic corrosion due to chlorine ions contained as impurities in the curing agent and epoxy resin. .

Silicone resin has a high moisture permeability, so its characteristics change depending on humidity. However, it has the disadvantages that its use in sub-components is limited, it has poor adhesion to metals and plastics, and it is expensive.

Polyurethane is also used as an alternative material to the above-mentioned epoxy resins and silicone resins. Since polyurethane is highly flexible, it can be used for electrical insulation as long as it has water resistance, low-temperature properties, and electrical properties, and can be used for a variety of other uses including civil engineering.

In order for polyurethane to have the above-mentioned properties, it is important to select the polyol component to be reacted with the polyisocyanate component, that is, the urethane polyol, and from this point of view, various studies on urethane polyols have been conducted.

For example, as a urethane polyol, (a) a polybutadiene polyol or its hydrogenated product (
Institute of Electrical Engineers of Japan Abstracts, page 211 [1978]).

(b) those using castor oil or its derivatives (JP-A-57-85816, JP-A-57-87417, U.S. Pat. No. 3,362,921), (C) polybutadiene polyol or hydrogenation thereof and castor oil or its derivatives (JP-A-55-139422, JP-A-56-57818)
(Japanese Patent Laid-Open No. 58-93717) have been proposed.

The present applicant also proposes (i) a transesterification product of castor oil (A) and a natural oil or fat (B) having substantially no hydroxyl groups, or a combination of the transesterification product and a high viscosity hydrocarbon polyol ( JP-A No. 59-226016), (Portrait) A functional t@ group number 1.5 to 1.5 obtained by reacting a high viscosity hydrocarbon polyol (A), a polyhydric alcohol, and a monobasic acid or a dibasic acid. A patent application has been filed regarding the combination use of No. 3 with ester polyol (B) (Japanese Patent Application Laid-Open No. 60-215012). Note that in the above, a typical example of the high viscosity hydrocarbon polyol is polybutadiene polyol.

In addition, JP-A-54-61295 discloses a urethane foam made by mixing and foaming a dimer acid derivative polyol or (and) a castor oil derivative polyol, a hydrocarbon substance, a blowing agent, and a polyisocyanate. JP-A-54-160495 discloses a polyurethane foam sealing agent obtained from a dimer acid derivative polyol, a castor oil derivative polyol, or castor oil, or a mixture thereof and a polyisocyanate compound.

Problems that IJ1 aims to solve Among the above methods, the method of using polybutadiene polyol as the urethane polyol provides excellent electrical insulation, water resistance, and low-temperature properties, but due to its high viscosity, casting and defoaming are difficult. However, there are problems in that workability during impregnation is poor, and since the degree of unsaturation is high, it is susceptible to oxidative deterioration and has poor heat resistance. Furthermore, there is also the problem that a characteristic rubber odor is generated during cast molding, which worsens the working environment.

In order to improve workability in urethane systems using polybutadiene polyol, it is necessary to lower the viscosity by using a plasticizer in combination, but the combination of plasticizers is important because it prevents changes over time due to bleeding and electronic components. There is a risk of damage to the cured product, leading to a decrease in the physical properties of the cured product.

It has also been proposed to use a reactive diluent instead of a plasticizer, but commercially available reactive diluents have a high OH value, which impairs the properties of polybutadiene polyols.

Even with the addition of plasticizers and reactive diluents, the disadvantages remain based on the degree of unsaturation of polybutadiene polyol. Polybutadiene polyols that are hydrogenated to reduce the degree of unsaturation have even higher viscosity, making it impossible to use them in general.

Although castor oil has a low viscosity and good water resistance and electrical properties, it has a high OH value of about 160 mgKOH/g, making it impossible to obtain a low-hardness cured product with good low-temperature properties.

A transesterification product of castor oil and a natural oil or fat that has virtually no hydroxyl groups is bifunctional (about 120 mgKo I/g in OH value) in order to be used as a urethane polyol.
Since the above is required, it is not possible to further modify the water-poor base toxin, and it is not possible to provide a cured product with low-temperature properties and low hardness. The same applies to other castor oil derivatives.

As castor oil derivatives, esterified products of castor oil fatty acids and polyether polyols and alkylene oxide adducts of castor oil are also known, but those containing ether bonds are said to have poor water resistance and electrical insulation properties. There are drawbacks.

The method of using polybutadiene polyol or its hydrogenated product in combination with castor oil or its derivatives has limitations on the compatibility of the two, and the polyurethane after curing only exhibits properties intermediate between the two, resulting in a wood-like property. It's not a real improvement.

Dimer acid derivative polyols (typically polyester polyols synthesized from dimer acid and ethylene glycol) generally have extremely high viscosity, which limits their uses. Even when a dimer acid derivative polyol and a castor oil derivative polyol are used together, it is impossible to lower the viscosity while keeping the OH value low.

In addition, in Japanese Patent Application Laid-open No. 54-61295, dimer m
As a derivative polyol, there is mention of "dimer acid polyester, which is a reaction product of dimer acid and a long-chain polyol, such as castor oil" (page 2, bottom left column 8-11).
According to research conducted by the present inventors, this product has a viscosity as high as that of polybutadiene polyol, and it is impossible to reduce the viscosity while keeping the OH value low.

The present invention provides a urethane polyol that solves the above-mentioned problems, that is, it has a viscosity that is easy to handle,
The purpose of this work is to provide a urethane polyol from which a polyurethane with low water absorption and excellent electrical insulation can be obtained.

Means for Solving the Problems In order to solve the above problems, various compounds were synthesized and their usefulness as urethane polyols was investigated. base 2.5
The following (especially 1.3 to 2.4) castor oil-based polyols (
It was discovered that a polyester polyol consisting of an esterified product of 1 or 2 moles of Y) and 1 or 0 moles of a polyol (Z) other than the castor oil-based polyol (Y) was useful for this purpose, and the present invention was completed. I ended up doing it.

The present invention will be explained in detail below.

Dimer acid (X) refers to a dimer obtained by polymerizing unsaturated fatty acids such as linoleic acid, oleic acid, elaidic acid, and tall oil fatty acid. Generally, the main component is a dicarboxylic acid with 36 carbon atoms because the raw material is a fatty acid with 18 carbon atoms, but those produced industrially contain some trimers and monomers.

Castor oil polyol (
Y) is: ■ Partially dehydrated castor oil; ■ Partially acylated castor oil.

A compound selected from the following groups is used: (1) a transesterification product of castor oil and a natural oil or fat having substantially no OH groups, and (2) an ester of castor oil fatty acid with a low molecular weight polyol.

Partially dehydrated castor oil is made by extracting castor oil from sulfuric acid, phosphoric acid, p-)
Obtained by heating in the presence of an acidic catalyst such as luenesulfonic acid.

Partially acylated castor oil is obtained by partially acylating castor oil. Among the acylations, acetylation is the most important, and industrially it is practically limited to this acetylation. As the acetylation method, a method of reacting with ketene or a method of reacting with glacial acetic acid can be adopted, but acetylation with acetic anhydride is industrially most advantageous.

Examples of transesterification products between castor oil and natural fats and oils that do not substantially have OH groups include transesterification reactions that are commonly carried out between the two, such as alkali catalysts such as alkali hydroxide, alkali metal alcoholades, and sodium carbonate. A method is adopted in which the transesterification reaction is carried out under reaction conditions of 180 to 260° C. for 15 minutes to 6 hours in the presence of a catalyst.

In addition, the natural oils and fats that do not substantially contain OH, 75 mentioned above include linseed oil, tung oil, rapeseed oil, soybean oil,
Examples include vegetable oils such as coconut oil, palm oil, edible oil, walnut oil, rice bran oil, cottonseed oil, camellia oil, olive oil, and arachis oil, and animal oils such as beef tallow, lard, fish fat, liver oil, and whale oil.

Examples of esters of castor oil fatty acids with low molecular weight polyols include esterification products of castor oil and low molecular weight polyols, and esterification products of castor oil fatty acids or their alkyl esters and low molecular weight polyols.

Here, examples of the low fraction 1 polyol include ethylene glycol, propylene glycol, dipropylene glycol, 1
．． 4-butanediol, neopentyl glycol, 1,
Polyols such as 6-hexane glycol, polypropylene glycol, glycerin, trimethylolpropane, pentaerythritol, sorbitol, multifunctional polyether polyol, or alkylene oxide (ethylene oxide, propylene oxide, butylene oxide, etc.) adducts of these polyols, etc. can be exemplified.

The above-mentioned castor oil polyol (Y) is one in which the number of functional groups per molecule is 2.5 or less, particularly 2.4 or less, in any case of ■, ■, ■, or ■. . If the number of functional groups per molecule exceeds 2.5, it becomes substantially equivalent to castor oil and the viscosity of the ester with dimer acid (X) increases, making it impossible to fully achieve the purpose of the present invention. .

On the other hand, if the number of functional groups per molecule is extremely reduced, it will essentially become a monool, so there is a natural restriction on the lower limit, which is usually 1.3 or more, particularly 1.4 or more.

By the way, castor oil is a triglyceride whose main component is ricinoleic acid, and its constituent fatty acids account for about 90% by weight.
is ricinoleic acid, and most of the remaining fatty acids are OH
Since it does not have any groups, the number of functional groups of castor oil is about 2.7 (OH value is about 160 mgKOH/g).

Polyols (Z) other than the above castor oil polyol (Y)
) as castor oil, ethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol, neopentyl glycol, 1,6-hexane glycol, polypropylene glycol, glycerin, trimethylolpropane, pentaerythritol, sorbitol, Examples include polyols such as polyfunctional polyether polyols, and alkylene oxide (ethylene oxide, propylene oxide, butylene oxide, etc.) adducts of these polyols.

The polyester polyol of the present invention has dimer acid (X)
1 mol, 1 mol or 2 mol of the above-mentioned castor oil polyol (Y), and 1 mol or 0 mol of a polyol (Z) other than the castor oil polyol (Y). Of these, the most important one is dimer acid (X
) and 2 moles of castor oil polyol (Y).

The esterification reaction can be achieved by heating the above components in an inert gas atmosphere without a catalyst or in the presence of a metal catalyst or an acidic catalyst.
250°C, especially 180-240°C, reaction time 2-240°C.
It is often about 24 hours.

The amount of castor oil polyol (Y) to be used per mole of dimer acid (x) is equivalently 1 mole or 2 moles, but a width of about 0.5 to 2.5 moles is acceptable. Similarly, the amount of polyol (Z) other than castor oil polyol (Y) to be used per 1 mol of dimer acid (X) is currently 1 mol or 0 mol, but it is about 1.5 to 0 mol. width is allowed. This is because within this range, although by-products or unreacted products are produced, the desired polyester polyol is produced in the required amount.

The ester polyol of the present invention consisting of the above-mentioned esterified product can be used for various purposes, but it can also be used as a polyol component (that is, a urethane polyol) for reacting with a polyisocyanate component in a two-component urethane system.
It is particularly useful as a In this case, other known urethane polyols such as castor oil can also be used together with the polyester polyol of the present invention.

Polyisocyanate components in the urethane system include diphenylmethane diisocyanate (MDI),
Polymerized MDI, carbodiimide modified MDI, tolylene diisocyanate, naphthalene diisocyanate, xylene diisocyanate, diphenylsulfone diisocyanate, triphenylmethane diisocyanate,
Hexamethylene diisocyanate, 3-incyanate methylcyclohexyl diisocyanate, diphenylpropane diisocyanate, phenylene diisocyanate, cyclohexylene diisocyanate, 3.3°-diisocyanate dipropyl ether, triphenylmethane triisocyanate, infron diisocyanate,
Used are diphenyl-4,4'-diisocyanate, 1,8-diisocyanate-4-isocyanate methyloctane, or terminal isocyanate prepolymers obtained by reacting these polyisocyanates with polyols or monools.

The blending ratio of polyol and polyisocyanate during the urethanization reaction is such that the ratio of OH groups in the polyol to NGO groups in the polyisocyanate, NC010H, is 0.8.
It is preferable to set it within the range of 1.4 to 1.4 because sufficient curing can be achieved.

Curing may be performed at room temperature or under heating.

In the urethanization reaction, fillers or pigments, flame retardants, curing accelerators, crosslinking agents, catalysts, antifoaming agents, thixotropes, plasticizers, solvents, antioxidants, ultraviolet absorbers,
Additives such as leveling agents can be added.

A two-component urethane system using the polyester polyol of the present invention alone or in combination with other known polyols as a urethane polyol can be used in electrical insulation, adhesives, paints, sealants, sealants, linings, flooring materials, moldings, etc. It is useful for a variety of purposes including things.

Function: As mentioned above, the polyester polyol of the present invention contains 1 mole of dimer acid (X) and a functional group a per molecule.
It consists of an esterified product of 1 mol or 2 mol of a castor oil-based polyol (Y) of 2.5 or less and 1 mol or 0 mol of a polyol (Z) other than the castor oil-based polyol (Y).

As a typical example, dimer acid (X) is converted into HOOC-R-
COO)I, castor oil polyol (Y) is lo-R'-OH, and polyol (Z) other than castor oil polyol (Y) is lo-R''-OH, then 1 mole of (X) is ( If 2 moles of Y) react, polyester polyol HO-R'-00C-R-Coo-R"-OH will be obtained, and if 1 mole of (Y) and 1 mole of (Z) react with 1 mole of (X), For example, polyester polyol 10-R'-00C-
R-000-R"-OH is obtained.

During urethanization, this terminal OH group reacts with the NGO group of the polyisocyanate compound.

Example Next, the present invention will be further explained with reference to Examples.

Hereinafter, "parts" and "%" are expressed on a weight basis.

L soil eni 1 Dimer acid: 75% dimer, 20% trimer
%, has a composition of 5%, and has an acid value of 193 mgK.
OH/g, specific gravity 0.95/25℃, viscosity 9000cp
A commercially available dimer acid at s/25°C was used.

castor, polyol A primary castor oil polyol was prepared.

(Y-1) Partially dehydrated castor oil 600 parts of castor oil and 0.9 parts of acidic sodium sulfite were charged into a flask equipped with a thermometer and a stirrer.

Heat under reduced pressure. The dehydration reaction started at 165 to 190°C, and then the temperature was gradually increased. 190-250℃, 1
The reaction was completed within a few hours, and after cooling, acid clay was added at 150° C. for purification by filtration. As a result, 08 valence 120 mgKO
Partially dehydrated castor oil with a viscosity of 450 cps/25°C was obtained.

(Y ~ 1°) Partially dehydrated castor oil Example 1, only the reaction time was changed,
Partially dehydrated castor oil with mgKOH/g and a viscosity of 580 cps/25°C was obtained.

(Y-2) Partially Acylated Castor Oil 600 parts of castor oil and 35 parts of acetic anhydride were charged into a flask equipped with a thermometer, a stirrer, and a reflux condenser.
The reaction was continued for about 2.5 hours by heating to 0-150°C. Then, the reflux condenser was replaced with a distillation condenser, and the temperature was gradually raised, and by-produced acetic acid and unreacted acetic anhydride were distilled and recovered. During this time, the degree of vacuum was gradually increased using an aspirator. The temperature of the system reached 230°C after 1 hour, so it was kept at this temperature for 1 hour and then cooled. As a result, the 08 value is 125 mg KO) 1 part g, the viscosity is 400 cps/2
Partially acetylated castor oil at 5°C was obtained.

(Y-3) Transesterification product of castor oil and natural fats and oils having substantially no OH groups 200 parts of castor oil and rapeseed oil (acid value 0.1, pour point -1
7,5°C) and 100 parts of sodium methylate.
4% at 230-240°C with 0.6 parts of methanol solution.
After reacting for an hour, the mixture was cooled, neutralized with phosphoric acid (first class reagent), and purified by filtration at 120° C. by adding activated clay.

As a result, 08 valence 107 xrgKOH/g, viscosity 2
A castor oil-rapeseed oil transesterification product was obtained at 42 cps/25°C.

(Y~4) Ester of castor oil fatty acid with low molecular weight polyol After reacting 300 parts of castor oil fatty acid and 61 parts of ethylene glycol at 150 to 200°C for 8 hours, cooling, and then adding activated clay at 120°C. It was purified by filtration. As a result, the 08 value was 265 mgKOH/g, and the viscosity was 265 c.
Ethylene glycol monolysyllate of ps/25°C was obtained.

(Yo) Castor oil OHH value 16.8mgKOH/g, viscosity 680 cp
Castor oil at s/25°C was used.

Example 1 582 g (1 mol) of the above dimer, 1 OH value of the above mentioned dimer
20g KOH/g partially dehydrated castor oil (Y-1) 18
60 g (2 mol) and 2.4 g (0.1% based on the system) of the tin-based catalyst were charged into a Mitsuro flask equipped with a thermometer and a stirrer, and reacted at 220°C for 8 hours. After cooling, [2
The mixture was purified by filtration by adding acidic clay at 0°C. This reaction resulted in an acid value of 2.8 mgKOH/g and an OHH value of 445 mgKO.
A polyester polyol with a viscosity of 5080 cps/25° C. was obtained.

Example 2 582 g (1 mol) of the above dimer acid, 140 mg KOH/g partially dehydrated castor oil (Y-1'
) 1860 g (2 mol) and 2.4 g of tin-based catalyst
(0.1% based on the system) was charged into a flask and heated to 220°C.
After cooling for 12 hours, acid clay was added at 120° C. for purification by filtration. This reaction resulted in an acid value of 1.8+sgK
A polyester polyol having an OH/g, an OH value of 48.8 ggKOH/g, and a viscosity of 6380 cps/25°C was obtained.

Example 3 582 g (1 mol) of the above dimer acid, 125 mg KOH/g partially acetylated castor oil (Y
-2) 1860g (2 mol) and tin-based catalyst 2.4
g (0.1% based on the system) into a flask, 220
The reaction was carried out at 160°C for 16 hours, and after cooling, acid clay was added at 120°C for purification by filtration. This reaction resulted in an acid value of 4.3 mgK.
A polyester polyol having an OH/g, an O8 value of 42.2 gKOH/g, and a viscosity of 4880 cps/25°C was obtained.

Example 4 582 g (1 mole) of the above dimer acid and 832 g (2 mole) of the above ethylene glycol monolysyllate (Y'-4) with an OH value of 265 mgKOH/g were charged into a flask and heated at 220°C for 15 hours. Let it react.

After cooling, acid clay was added to the mixture at 120° C. for purification by filtration. This reaction resulted in an acid value of 2.3 gKOH/g and an OH value of 7.
9.0+wgKOH/g, viscosity 3100 cps/2
A polyester polyol at 5° C. was obtained.

Example 5 9582 g (1 mol) of the above-mentioned dimer, 1840 g' (2 mol) of castor oil-rapeseed oil transesterification product (Y-3) of 1/g OH value 107 mg KO), and 1.4 g of tin-based catalyst. (0.1% based on the system) was charged into a flask, reacted at 220°C for 15 hours, and after cooling, the temperature was increased to 120°C.
It was filtered and purified by adding acid clay.

This reaction resulted in an acid value of 2.8+sgKOH/g, O
H number 45.0mgKOH/g, viscosity 4300 cps
/25°C polyester polyol was obtained.

Example 6 1160 g (2 mol) of the above dimer acid, partially dehydrated castor oil (Y-1) 1 with the above OH value of 120 gKOH/g
830g (2 moles) and 236g hexanediol (
2 mol) into a flask, reacted and purified in the same manner as in Example 1, resulting in an acid value of 2.3 gKOH/
g, O8 value 42. l gKOH/g, viscosity 610
A polyester polyol of 0 cps/25°C was obtained.

Comparative Example 1 2 g (1 mol) of the above dimer acid 5B and 800 g (2 mol) of polypropylene glycol having a molecular weight of 1400 were charged into a flask, reacted at 220°C for 6 hours, and after cooling, 1
The mixture was purified by filtration at 20°C by adding acidic clay. This reaction resulted in an acid value of 2.8 gKOH/g and an OH value of 80.2 mgK.
A polyester polyol with a viscosity of 1530 cps/25° C. was obtained.

Comparative Example 2 1746 g (3 moles) of the above dimer acid, 248 g (4 moles) of ethylene glycol, and 2.0 g of tin-based catalyst
(001% based on the system) was charged into a flask and reacted at 220°C for 8 hours.The viscosity of the 0 reaction product was 100,000 cps.
/25°C or higher.

Comparative Example 3 582 g (1 mol) of the above dimer acid, 124 g (2 mol) of ethylene glycol, and 0.7 g of tin-based catalyst (
0.1% of the system) into a flask, and heated at 220℃ for 8
The viscosity of the reactant reacted for 0 hours is l 00000 cp
s/25°C or higher.

Comparative Example 4 The above dimer 1% i582g (1 mol) and the above 08
Castor oil (B') 1860 with value 78.8mgKOH/g
g (2 mol) into a flask and reacted at 220°C for 12 hours, and after cooling, acid clay was added at 120°C and purified by filtration. This reaction resulted in an acid value of 2.7 mgKOH/g.
A polyester polyol with an OH number of 7B, 13 mgKOH/g, and a viscosity of 762°cps/25°C was obtained.

Comparative example 5 A commercially available polybutadiene polyol was prepared.

The acid value was 0.1 gKOH/g or less, the OH value was 48.0 gKOH/g, and the viscosity was 7800 cps/25°C.

Examples 1-6. The characteristic values of the polyester polyols or polyols obtained in Comparative Examples 1 to 5 are summarized in Table 1.

Table 1 As shown in Examples 1 to 6 above, the polyester polyol of the present invention has a viscosity that allows it to be easily handled as a urethane polyol.

<Urethanization reaction> The polyester polyols or polyols obtained in Examples 1 to 6 and Comparative Examples 1.4 and 5 and carbodiimide-modified diphenylmethane diisocyanate (Millione MTL, manufactured by Kuchigi Polyurethane Kogyo Co., Ltd.) were combined into N COlo
Blended at a ratio of H = 1.05, mixed and stirred, poured into a mold after defoaming, and cured at a temperature of 120°C for 1 hour to a thickness of 3.
A layered cured sheet was obtained.

The physical properties of this cured urethane product are shown in Table 2 below.

Table 2 Note 1. Abnormal odor refers to the presence or absence of an abnormal odor (rubber odor) during curing work.

Note 2. In Comparative Example 5, if a polybutadiene polyol that provides a polyurethane with a low hardness of about 20 A is selected, the viscosity will be several tens of thousands of cps/25°C.

Effects of the Invention The polyester polyol of the present invention has a viscosity that is easy to handle, and a urethane system using it as a urethane polyol provides a polyurethane with low water absorption and excellent electrical insulation properties. Also, no strange odor is generated during the heating process.

In addition, the hardness of the obtained polyurethane can be reduced, and even if a plasticizer is added, the amount of heat can be reduced, so that disadvantages due to the addition of a plasticizer can be minimized.

Patent applicant: Ito Oil Co., Ltd.

Claims (1)

[Claims] 1. 1 mole of dimer acid (X), 1 mole or 2 moles of castor oil polyol (Y) having 2.5 or less functional groups per molecule, and other than the castor oil polyol (Y) A polyester polyol consisting of an esterified product of 1 mole or 0 mole of polyol (Z). 2. The polyester polyol according to claim 1, wherein the castor oil polyol (Y) has a functional group number of 1.3 to 2.4 per molecule. 3. 1 mole of dimer acid (X) and number of functional groups per molecule: 2
．． The polyester polyol according to claim 1, comprising an esterified product with 2 moles of castor oil-based polyol (Y) of 5 or less. 4. Castor oil-based polyol (Y) is a transesterification product of (a) partially dehydrated castor oil, (b) partially acylated castor oil, and (c) castor oil with a natural oil or fat having substantially no OH groups. , and (d) an ester of castor oil fatty acid with a low molecular weight polyol. 5. The polyester polyol according to claim 1, which is used for urethane polyol.